If you check the word "best" in a dictionary, then you will find that it can play different roles in sentences. One of them is Adverb
In Oxford we can read:
Best: To the highest degree; most (used with verbs suggesting a desirable action or state or a successful outcome)
It demonstrates the definition by providing this example:
well-drained soil suits this plant best.
So, I agree with you (as a learner) that "gold" is a typo and therefore, the suggestion seems to be valid.
I should say that, there is no significant problem with the "best of all". Personally, I think the "of all"-free version is more terse and probably that's the reason why the author suggested omitting that part. As stated above, best already means to the highest point.